Li ion accumulators are distinguished by a high energy density and are heat-stable. The terms accumulator and battery are used as equivalent in the following. Graphite or lithium titanate is usually used as the negative electrode (anode). Lithium-containing compounds, in particular lithium metal oxides or lithium phosphates, are used as the positive electrode (cathode). The following materials in particular are known as the active electrode material: LiCoO2, LiNiO2, LiNi1-xCoxO2, LiNi0.85Co0.1Al0.05O2, LiNi0.33Co0.33Mn0.33O2, LiMn2O4, LiFePO4, Li3V2(PO4)3, LiMnPO4 and LiV3O8.
Li ion accumulators are classified further according to the electrode materials employed into lithium cobalt dioxide accumulators (LiCoO2), lithium-manganese accumulators, lithium iron phosphate accumulators (LiFePO4) and tin-sulphur-lithium ion accumulators. Lithium iron phosphate is a widely used cathode material since it is distinguished by a high structural stability, low toxicity and relatively low costs (see Dinh in Electroanalysis 2011, 23, no. 9, page 2079). LiFePO4 has a moderate theoretical capacitance of 170 mAh/g and a stable voltage plateau of 3.45 V versus Li/Li+. Nevertheless, pure LiFePO4, like other lithium metal oxides also, is distinguished by a low electrical conductivity (10−9 S/cm for LiFePO4) and low ionic conductivity. This disadvantage can be compensated by the use of composite materials which, in addition to the lithium metal oxide, contain a material having a high conductivity. Carbon black, graphite and conductive polymers are known as the conductivity composite material.
The methods known to date for employing conductive polymers as the conductivity composite material are involved processes, since either the conductive polymers are polymerized on the cathodes, or combinations with further composite materials, such as, for example, carbon black or carbon fibres, are necessary.
For example, composite materials in which polypyrrole has been deposited on LiFePO4 are known. The use of this material as the cathode in an Li ion accumulator leads to an increased current capability (see Fedorkova et al. in Electrochim. Acta 55, 2010, page 943). LiFePO4/polyaniline cathodes in turn are distinguished by an increased cycle stability (see Chen et al. in Electrochim. Acta, 56, 2011, page 2,689). It is furthermore known that LiFePO4/PEDOT composite materials improve the current capability and cycle stability (see Dinh et al. in ECS Transactions 28, 2010, page 167).
In JP 2004-158286 composite materials of MoO3 and PEDOT are prepared and tested as an electrode, the PEDOT first being deposited as a precipitate and then being mixed with the MoO3. (PEDOT)/LiCoO2/carbon fibre composite materials which achieve an improved cycle stability and electrochemical stability compared with cathodes without a conductive polymer are furthermore known.
JP 2011-100594 describes the use of complexes of PEDOT and a sulphonated polymer in the presence of a carbon-based conductivity additive based on carbon-containing substances, such as, for example, carbon black, for use in Li ion accumulators. For this the conductive monomer can be polymerized by chemical or electrochemical means. It is then precipitated and redissolved.